Migrating from nixos-generators module to nixos-rebuild build-image

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Hi

I previously used the nixos-generators module in my flake to create a qcow2 disk which i imported in proxmox and created vm’s with.
I am now trying to migrate to nixos-rebuild build-image but i get a disk mount error.

Screenshot_20260219_163525
Screenshot_20260219_1635252119×1193 226 KB

This is from a simple flake i created to minimize potential errors. I don’t have any filesystem mounts in the config because i didn’t need them before and when i tried it i couldn’t get it to work.

My flake.nix and configuration.nix

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
  };

  outputs = {
    nixpkgs,
    ...
  }:{
    nixosConfigurations = {
      nixos = nixpkgs.lib.nixosSystem {
        system = "x86_64-linux";
        modules = [
          ./common.nix
        ];
      };
    };
  };
}

{...}:
{
  services.openssh.enable = true;
  services.qemuGuest.enable = true;
  security.sudo.wheelNeedsPassword = false;
  users.users.nixos = {
    isNormalUser = true;
    openssh.authorizedKeys.keys = [
      "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIPwq+TcTSfAMKHyYKB9O3F9iGbhZvXzXAIwmSDTf6nYY"
    ];
    extraGroups = ["wheel"];
  };
  system.stateVersion = "25.11";
}

Thanks!